1. Technical Field
The present invention relates generally to digital communication and more specifically to communications over power lines.
2. Discussion of the Related Art
In the last years the broadband wireless mobility and the machine-to-machine communications were considered as markets to enable an important economic growth. The wireless and M2M (machine-to-machine) services, including the Smart Grids communication, require ubiquitous deployment for satisfying the user requirements for these services.
While the power line is a natural media for ubiquitous coverage for fixed M2M and Smart Grid applications, the wireless coverage is limited by obstacles and the wall penetration. The PLC (Power Line Communication) is used for data communication on already significant distances, targeting to compete with other broadband access technologies, as ADSL, Cable modem, Fixed and Mobile Cellular. PLC is also the natural form for connecting the in-house Smart Grids or for being used in other M2M (Machine-to-Machine) applications, due to the ubiquitous presence of the AC power supply.
The 3G-4G cellular technologies enjoy the broadband and mobility properties, but they have the problem of outdoor-to-indoor penetration, especially into those isolated places where the Smart Grid sensors and meters are placed. In addition, the broadband cellular technologies, as LTE, have a serious problem in supporting a very high number of machine-type terminals (MT) in their cell coverage area.
While U.S. Pat. Nos. 6,243,571 or 7,269,403 describe the possibility of transmitting the wireless signals over the power line, they do not take into account that also the power line is a media with lots of interferences and there is need of a method to asses and avoid such interferences. US patent application 20070201540, considering hybrid power line and wireless media, discuss the interference and channel selection only for the wireless media.
MIMO operation in wireless cellular networks has been expanded in the last years to 8 antenna ports. However the US application 20080273613 is limited to only two antenna ports, because is using the existing phase, neutral and ground power lines.
The wireless technologies deployed in license-exempt bands have a limited coverage, due to the limitation of the transmitted radio power. In the last time, the digitally connected Remote Radio Head (RRH) technology, allowing to connect by optical fibers the remote radios, has received a special attention in 3GPP, due to the potential benefits of both coverage and increased data rates. However the optical fiber is not available in any place and the requested data rates around of 1 Gb/s per base station may be highly priced.
Another aspect to be considered is the potential negative impact of the mobile phones on the humans health, confirmed by an OMS (World Health Organization) study just published.